Alternative Control of Fluctuation Frequency in the Wake of a Rectangulay Cylinder near the Critical Shape

采用离散涡方法对均匀流中矩形圆柱体前缘吸力触发的完全分离流和周期性再附流交替控制进行了数值模拟。根据数值模拟的结果，在前缘带有吸气槽的矩形圆柱体上连接了吸气速度和工作时间可控的吸气装置，然后进行了实验。通过数值模拟和实验得到的主要结果如下：1.在临界形状圆柱体绕流中，小侧高比圆柱体绕流出现了完全分离的脉动，大侧高比圆柱体出现了周期性的再附流。它们在实验中间歇性地出现，而在模拟中出现叠加波形。2.在数值模拟中，…在运行时间内，通过单次吸力将更多的流量转移到周期性再附流中，吸力的速度是入射流的0.4~0.7倍，完全分离流的波动周期为其的1/30，经过一段时间后，转移的流量恢复到临界流。吸气宽度以气缸高度的一半为宜。在数值模拟中实现临界形状的侧高比在3.6~4.0范围内是可能的。3.在实验中，低雷诺数时的临界形状为2.7，高雷诺数时为2.3。计算结果在定性上与数值模拟结果基本一致，但在定量上出现了一些差异，如完全分离流动的运行时间比数值结果高0.7~1.0倍，波动周期长0.1~0.4倍，吸力控制的宽度应在0.2倍高度以下。4.上述差异以及吸力后少数几个时间段出现滞后转变等问题有待研究。较少

Numerical simulation by discrete vortex method was carried out on the alternative control between wholly separated flow and periodically reattached flow, triggered off by suction at a leading edge of a rectangular cylinder near the critical shape in a uniform flow. Experiments were executed after preparing rectangular cylinders with the suction slot at the leading edge connected to a suction device in which suction speed and operating time were controllable, based on the results of the numerical simulation. The main results obtained through the simulation and the experiments are the following.1.In the flow around a cylinder with the critical shape, fluctuation in wholly separated flow appeared in the flow around a cylinder with small side-to-height ratio are superposed on periodically reattached flow appeared in the one with large side-to-height ratio. They appear intermittently in the experiment, while supperposed wave form appears in the simulation.2.In the numerical simulation, the … More flow was transferred to the periodically reattached flow by a single suction which had 0.4-0.7 times speed in the incident flow and 1/30 of fluctuating period in the wholly separated flow for the operating time, and the transferred flow returned to the critical flow after a while. The suction width with a half of the height of cylinder was suitable to the transition. This control was possible in the range of side-height ratio between 3.6 and 4.0 at which the critical shape was realized in the numerical simulation.3.In the experiment, the critical shape was realized at 2.7 of side-height ratio at low Reynolds number and 2.3 at high Reynolds number. The results were similar qualitatively to those of the numerical simulation, but, quantitatively, some differences appeared such as the transition occurred at 0.7-1.0 times of the suction speed higher and for 0.1-0.4 times fluctuating period in the wholly separated flow of operating time longer than the numerical results, and the suitable width for the suction control was below 0.2 times the height.4.We have some problems to be investigated such as the differences above-mentioned and the retarded transition occurred at a few periods after the suction. Less